The present invention relates to the improvement of a veneer lathe to cut off veneer sheets from a log.
In a conventional veneer lathe, a driving force is transmitted to the butt ends of a log through the chucks of a spindle which grips the butt ends of the log directly. In such a veneer lathe, since the diameter of the chuck is smaller than the diameter of the log, the gripped butt ends of the log can not withstand the cutting resistance applied to the log by the cutting knife, so that the gripped butt ends are twisted off or fractured frequently. Thus such a conventional veneer lathe has a disadvantage that most logs cannot be cut down to an intended diameter (usually 100 mm for a log of 1 m in length).
The applicant of the present invention developed and proposed a new veneer lathe such as disclosed in Japanese Patent Publication No. 56-16729 in order to overcome the disadvantage of the conventional veneer lathes. The new veneer lathe proposed by the applicant of the present invention, comprises a rotary roller having a plurality of annular driving members each having a plurality of spikes arranged along the circumference thereof, said driving members being attached to the roller at suitable intervals along the axial direction of the rotary roller, said rotary roller being disposed substantially in parallel to an edge of the cutting tool and so as to enable the spikes to thrust into the circumference of a log at a position near the edge of the cutting knife, a driving unit for driving the rotary roller and a pressure member, such as a fixed bar or a roller, disposed on at least one side of each driving member, to wit, in some of a plurality of spaces formed between the driving members of the rotary roller.
Since driving force is applied to a log at the circumference thereof near the edge of the cutting knife through the driving members of the rotary roller in cutting the log on the above-mentioned new veneer lathe, damage to the log resulting from the concentration of stress on the gripped part of the log, which is likely to occur in cutting a log on a conventional veneer lathe, occurs scarcely. Additionally, a trouble that a space between the pressure members and a log is clogged with foreign matters such as the bark of logs and pieces of wood and damage to logs resulting from such a trouble are avoided and almost all logs can be cut down to a conventionally intended diameter to produce superior veneer sheets, so that many logs are cut into veneer sheets remarkably effectively as compared with log cutting on conventional veneer lathes.
The outside diameter of a stripped core of about 100 mm for a log of 1 m in length was a desirable outside diameter at the times when logs of comparatively large diameters were available comparatively easily. However, such an outside diameter is not necessarily said to be sufficiently reduced in recent years, when logs of large diameters are not easily available, much less in the future when the diameter of available logs will be reduced still further and hence a further reduction of the outside diameter of the stripped core will be necessary.
As well known, the rigidity of wood in general is considerably low as compared with those of metals and the deflection of a cylindrical body varies in proportion to a function of the fourth power of the diameter and the third power of the length. Therefore, when the outside diameter of the stripped core is reduced below 100 mm, the rigidity is reduced sharply with the result that the log is broken or that a veneer sheet of uneven thickness unsuitable for use is produced due to considerably increased deflection of the log. Furthermore, the spikes of the driving member are required to be thrusted deeper into the circumference of a log to prevent the sharp reduction of the engagement between the circumference of the log and the driving members of the rotary roller as the diameter of logs becomes smaller. The presence of cracks caused by stress and radiating from the core (the heart of the log) also promote damage to logs. Accordingly, even the above-mentioned new veneer lathe is incapable of cutting a log easily to a smaller diameter merely by reducing the outside diameter of the spindles and thereby is incapable of coping with expected difficult availability of suitable logs.